CN104993706B - A current sharing control system and method for parallel connection of two-module DC-DC converters - Google Patents

Abstract

The invention discloses a current sharing control system and method for parallel connection of two-module DC-DC converters, including two DC-DC converters whose input ends are connected in parallel and whose output ends are connected in parallel. The difference between the output voltage of the DC-DC converter and the reference voltage is sent to the voltage regulator, and the voltage regulator will adjust the phase-shifting duty cycle of the converter according to the disturbance and send the signal to the parameter measurement module. The parameter measurement module The parameters related to the output current are obtained according to the variation of the phase-shift duty cycle of the two DC-DC converters and sent to the compensation amount calculation module; the compensation amount calculation module pairs the corresponding DC-DC converter according to the parameters related to the output current Compensate for parameter mismatch between modules, and realize output current sharing of two DC-DC converters. The invention does not require a current transformer to sample the current of each module, which greatly simplifies the complexity of the control and reduces the cost at the same time.

Description

A current sharing control system and method for parallel connection of two-module DC-DC converters

technical field

The present invention relates to the technical field of power electronics, to related technologies of parallel connection of input and output of two modules in the field of DC-DC converters, and in particular to the technology of parallel current sharing without current transformers of DC-DC converters.

Background technique

With the development of science and technology, large-capacity power supply systems are more and more widely used, which puts forward higher and higher requirements for the voltage and current level, capacity and power density of DC-DC converters. The DC-DC converter input parallel connection and output parallel connection can improve the power level of the entire combined converter, and at the same time, the transformer capacity and the current stress of the switch tube in a single DC-DC converter are still at a small value, ensuring the small size of the converter Lightweight and high efficiency, high power density. In addition, interleaved parallel control is adopted among the converters, which reduces the input and output current ripple, thus reducing the capacity and volume of the filter capacitor.

However, due to the influence of component tolerances, environmental changes and other factors, there will inevitably be differences in the component parameters of each module in the combined converter, which will lead to unbalanced current between modules, and make the switching devices bear different current stress and thermal stress. stress, thereby shortening the life of the switching device and reducing the efficiency and reliability of the entire converter. Therefore, the current sharing between modules has become one of the important research directions of the input-parallel-output parallel combined converter.

At present, there are two main types of current-sharing technologies for input-parallel-output parallel combined converters: the droop method and the active current-sharing method. The droop method achieves current sharing between modules by changing the output impedance of each module, and is mainly suitable for low-power applications. The active current sharing method requires the current detection unit to sample the current of each module, the control system is relatively complex, the cost is high, and the current sharing bus is highly sensitive to noise, which affects the current sharing effect.

In short, the current sharing technology of the current input-parallel-output parallel combination converter cannot meet the needs of the current large-capacity power supply system, and a new type of current sharing control system and method for parallel connection of two-module DC-DC converters is urgently needed .

Contents of the invention

In order to solve the deficiencies in the prior art, the present invention discloses a current sharing control system and method for parallel connection of two-module DC-DC converters. Current sharing between parallel modules.

To achieve the above object, the specific scheme of the present invention is as follows:

A current sharing control system for parallel connection of two-module DC-DC converters, including two DC-DC converter modules whose input ends are connected in parallel and output ends are connected in parallel, and is characterized in that, under voltage loop closed-loop modulation, the parallel DC -The difference between the output voltage of the DC converter module and the reference voltage is sent to the voltage regulator, and the voltage regulator will adjust the phase-shift duty cycle of the converter according to the disturbance and send the signal to the parameter measurement module, the parameter measurement module According to the variation of the phase-shift duty ratio of the two DC-DC converter modules, the parameters related to the output current are obtained and sent to the compensation amount calculation module; the compensation amount calculation module converts the corresponding DC-DC according to the parameters related to the output current The converter module compensates for the parameter mismatch between the modules, and realizes the output current sharing of the two DC-DC converter modules.

Further, the voltage detection circuit is used to detect the output voltage of the parallel connected DC-DC converter modules.

Further, the circuit structures of the two DC-DC converter modules are the same, and both include a first full-bridge bridge circuit, a high-frequency isolation transformer and a second full-bridge bridge circuit connected in sequence, and the high-frequency isolation transformer has Converted to the leakage inductance of the primary side, the input terminal and the output terminal of the DC-DC converter module are respectively connected in parallel with capacitors.

A current sharing control method for parallel connection of two-module DC-DC converters, comprising:

For each DC-DC converter module, a common duty cycle control is first adopted, that is, the phase-shifting duty cycle of each DC-DC converter module is the same, which is the output of the voltage loop regulator;

After the system is stable under the control of the common duty cycle, subtract a constant offset from the phase-shift duty cycle of the first DC-DC converter module, and take the constant bias as 40% of the common duty cycle, and at the same time Keep the closed-loop adjustment of the voltage loop, and after the system is stable, calculate the reduction of the phase-shift duty cycle of the first DC-DC converter module and the increase of the phase-shift duty cycle of the second DC-DC converter module, The total load current remains unchanged, and the parameters related to the output current are obtained;

According to the parameters related to the output current, the main module and the auxiliary module are selected. The phase-shift duty cycle of the main module is the output of the voltage loop regulator, and the phase-shift duty cycle of the auxiliary module is the output of the voltage loop regulator plus the inter-module Amount to compensate for parameter mismatch.

Each DC-DC converter module controls the output voltage by adjusting the phase-shift duty cycle, and the phase-shift duty cycle d is given by:

in, is the phase shift angle between the first full bridge and the second full bridge in the DC-DC converter module.

The parameters related to the output current are given by:

Among them, n ₁ and n ₂ are the transformation ratios of the transformers in the first and second DC-DC converter modules respectively, and L ₁ and L ₂ are the conversion ratios of the transformers in the first and second DC-DC converter modules respectively. The leakage inductance of the primary side, Δd ₁ is the reduction of the phase-shift duty cycle of the first DC-DC converter module, and Δd ₂ is the increase of the phase-shift duty cycle of the second DC-DC converter module .

According to the parameters related to the output current, when selecting the main module and the auxiliary module, if Then select the first DC-DC converter module as the main module and the second DC-DC converter module as the auxiliary module, that is, the phase shift duty cycle of the first DC-DC converter module is equal to that of the voltage loop regulator The output, i.e. d ₁ =D, the phase-shifted duty cycle of the second DC-DC converter module is given by:

d ₂ =d ₁ +Δd' (3)

Among them, Δd' is the compensation amount for the parameter mismatch between modules, which can be given by the following formula:

like Then select the second DC-DC converter module as the main module, and the first DC-DC converter module as the auxiliary module, that is, the phase shift duty cycle of the second DC-DC converter module is equal to that of the voltage loop regulator The output, i.e. _d2 = D, the phase shift duty cycle of the first DC-DC converter module is given by:

d ₁ =d ₂ +Δd (5)

Among them, Δd is the compensation amount for the parameter mismatch between modules, which can be given by the following formula:

Beneficial effects of the present invention:

The invention measures and calculates the parameters related to the output current of each module by disturbing the phase-shifting duty cycle of the converter, adjusts the phase-shifting duty cycle of each module according to the parameters, compensates the parameter mismatch between modules, and realizes the effective current sharing. The invention does not require a current transformer to sample the current of each module, which greatly simplifies the complexity of the control and reduces the cost at the same time.

Description of drawings

Fig. 1 is the main circuit topology principle diagram of the current sharing control method without current transformer of the present invention;

Fig. 2 is the schematic diagram of the control system of the current sharing control method without current transformer of the present invention;

Figure 3 shows the transformer primary side leakage inductance current waveform of each module when two modules are connected in parallel and adopt common duty cycle control;

Fig. 4 is the transformer primary side leakage inductance current waveform of each module when two modules are connected in parallel and adopt the current sharing control method of the present invention;

Figure 5 shows the output current waveform of each module when two modules are connected in parallel and adopt common duty ratio control;

Fig. 6 is the output current waveform of each module when two modules are connected in parallel and adopt the current sharing control method of the present invention.

detailed description:

The present invention is described in detail below in conjunction with accompanying drawing:

As an applicable circuit of the present invention, the main circuit of a combined converter composed of two DC-DC converter modules connected in parallel is composed of two dual active bridge DC-DC converter modules, as shown in FIG. 1 . Module 1 is composed of a full bridge circuit H _p1 , a high frequency isolation transformer T ₁ and a full bridge circuit H _s1 , the transformer T ₁ has a leakage inductance L ₁ converted to the primary side; module 2 is composed of a full bridge Type circuit H _p2 , high-frequency isolation transformer T ₂ and full-bridge bridge circuit H _s2 are connected. Transformer T ₂ has a leakage inductance L ₂ converted to the primary side; the input ends of the two modules are connected in parallel, the output ends are connected in parallel, and the input ends are connected in parallel The capacitor C ₁ is connected in parallel with the capacitor C ₂ at the output end.

A current sharing control method for parallel connection of two-module DC-DC converters. Firstly, the common duty cycle control is adopted. After the output voltage is stable, the phase-shift duty cycle of the disturbance converter is used to measure and calculate the output of each module. Current-related parameters, adjust the phase-shift duty cycle of each module according to the parameters, compensate for the parameter mismatch between modules, and achieve effective current sharing.

The specific process of the embodiment of the present invention is described in detail below:

The principle diagram of the control system of the present invention is shown in FIG. 2 , and the output of the voltage loop regulator is D. First, the common duty cycle control is adopted, the phase shift duty cycle of module 1 is the same as that of module 2, both are the output of the voltage loop regulator, ie d ₁ =d ₂ =D. After the system reaches a steady state, the output currents I _o1 and I _o2 of the two modules are given by the following formula:

Among them, n ₁ and n ₂ are the transformation ratios of transformers T ₁ and T ₂ respectively, L ₁ and L ₂ are the leakage inductance of transformers T ₁ and T ₂ converted to the primary side respectively, and f _s is the switching frequency.

While maintaining the closed-loop modulation of the voltage loop, adjust the phase-shift duty cycle of module 1 to the common duty cycle D minus a constant offset, and take the constant offset as 40% of the common duty cycle. After the system is stable , the phase-shift duty cycle of module 1 can be expressed as:

d ₁ =D-Δd ₁ (3)

Among them, Δd ₁ is the reduction amount of the phase-shift duty cycle of the first DC-DC converter module.

The phase shift duty cycle of module 2 can be expressed as:

d ₂ =D+Δd ₂ (4)

Among them, Δd ₂ is the increment of the phase shift duty cycle of the second DC-DC converter module.

Under the closed-loop control of the voltage loop, the total load current remains unchanged, therefore, the decrease of the output current of module 1 is equal to the increase of the output current of module 2. From this, the circuit parameters of module 1 can be calculated Circuit parameters with module 2 The ratio of , is given by:

like Then select module 1 as the main module and module 2 as the auxiliary module, so that the phase-shift duty ratio of module 1 is the output of the voltage loop regulator, that is, d ₁ =D, and the phase-shift duty ratio of module 2 d ₂ =d ₁ + Δd', where Δd' is the compensation amount for parameter mismatch between modules, given by the following formula:

After entering the steady state, the output currents of the two modules are equal to achieve current sharing between modules;

like Then select module 2 as the main module and module 1 as the auxiliary module, so that the phase-shift duty ratio of module 2 is the output of the voltage loop regulator, that is, d ₂ =D, and the phase-shift duty ratio of module 1 is d ₁ =d ₂ +Δd, where After entering the steady state, the output currents of the two modules are equal to realize current sharing among the modules.

3 to 6 are simulation waveforms of the current sensorless current sharing control method for parallel connection of two-module DC-DC converters according to the present invention. The simulation parameters are: input voltage V _in =30V, output voltage V _o =80V, load Ro=25Ω, switching frequency f _s =20kHz, output power P=256W. The transformer transformation ratio n ₁ of module 1 =1:3.1, leakage inductance L ₁ =23 μH; the transformer transformation ratio n ₂ of module 2 =1:3.1, leakage inductance L ₂ =28 μH. Fig. 3 and Fig. 5 are respectively the transformer primary side leakage inductance current waveform and output current waveform of each module when two modules are connected in parallel and adopt common duty cycle control; Fig. 4 and Fig. 6 are respectively two modules connected in parallel and adopt the current sharing control of the present invention The method is the transformer primary leakage current waveform and output current waveform of each module. It can be seen that due to the different parameters of each module, when the common duty ratio control is adopted, there is a significant deviation between the primary side leakage inductance current and the secondary side output current of each module, and the current cannot be well balanced. However, when the current sharing control method of the present invention is adopted, the average value of the leakage inductance current of the primary side of each module and the output current of the secondary side tends to be consistent, and an obvious current sharing effect is achieved.

Although the specific implementation of the present invention has been described above in conjunction with the accompanying drawings, it does not limit the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, those skilled in the art do not need to pay creative work Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims (8)

1. A current sharing control system for two DC-DC converters in parallel connection is characterized by comprising two DC-DC converter modules with input ends in parallel connection and output ends in parallel connection, and under the condition of voltage loop closed-loop modulation, the difference between the output voltage of the DC-DC converter modules in parallel connection and a reference voltage is sent to a voltage regulator, the voltage regulator regulates the phase-shifting duty ratio of the converters according to disturbance and sends a signal to a parameter measuring and calculating module, and the parameter measuring and calculating module obtains parameters related to output current according to the variable quantity of the phase-shifting duty ratio of the two DC-DC converter modules and sends the parameters to a compensation quantity calculating module; and the compensation quantity calculation module performs compensation of parameter mismatching between modules according to the DC-DC converter modules corresponding to the parameters related to the output current, so as to realize output current sharing of the two DC-DC converter modules.

2. The current sharing control system of claim 1, wherein the voltage detection circuit is configured to detect the output voltages of the parallel DC-DC converter modules.

3. The current sharing control system according to claim 1, wherein the two DC-DC converter modules have the same circuit structure, and each of the two DC-DC converter modules includes a first full bridge circuit, a high frequency isolation transformer and a second full bridge circuit connected in sequence, the high frequency isolation transformer has a leakage inductance converted to a primary side, and the input and output terminals of the DC-DC converter modules are respectively connected in parallel with a capacitor.

4. The control method of claim 1, wherein the control method is used for a current sharing control system with two parallel modules of DC-DC converters, and comprises the following steps:

firstly, controlling each DC-DC converter module by adopting a common duty ratio, namely the phase-shifting duty ratio of each DC-DC converter module is the same and is the output of a voltage loop regulator;

after the system is stabilized under the control of the common duty ratio, subtracting a constant offset from the phase-shifting duty ratio of the first DC-DC converter module, simultaneously keeping the closed-loop regulation of a voltage ring, after the system is stabilized, calculating the reduction of the phase-shifting duty ratio of the first DC-DC converter module and the increase of the phase-shifting duty ratio of the second DC-DC converter module, keeping the total load current unchanged, and obtaining parameters related to the output current;

and selecting a main module and an auxiliary module according to parameters related to the output current, wherein the phase-shifting duty cycle of the main module is the output of the voltage loop regulator, and the phase-shifting duty cycle of the auxiliary module is the compensation quantity obtained by adding the unmatched parameters between the voltage loop regulator and the modules.

5. The method as claimed in claim 4, wherein each DC-DC converter module controls the output voltage by adjusting a phase-shift duty cycle d given by:

wherein,is the phase shift angle between the first full-bridge and the second full-bridge in the DC-DC converter module.

6. The method as claimed in claim 4, wherein the output current related parameter is given by:

$\frac{X_1}{X_2}=\frac{n_1}{L_1}/\frac{n_2}{L_2}=\frac{-{\mathrm{\Δd}}_2^2+{\mathrm{\Δd}}_2-2{\mathrm{\Δd}}_2\·D}{{\mathrm{\Δd}}_1^2+{\mathrm{\Δd}}_1-2{\mathrm{\Δd}}_1\·D}---\left(2\right)$

wherein n is₁、n₂The transformation ratios, L, of the transformers in the first and second DC-DC converter modules, respectively₁、L₂Respectively, the leakage inductance, Delta d, converted to the primary side by the transformer in the first and second DC-DC converter modules₁Is a reduction of the phase-shifted duty cycle of the first DC-DC converter module, Δ d₂D is the output of the voltage loop regulator, an increment of the phase-shifted duty cycle of the second DC-DC converter module.

7. The method as claimed in claim 6, wherein the main module and the auxiliary module are selected according to the output current related parameters if they are selectedSelecting the first DC-DC converter module as the main module and the second DC-DC converter module as the auxiliary module, i.e. making the phase-shift duty ratio of the first DC-DC converter module as the output of the voltage loop regulator, i.e. d₁D, the phase-shifted duty cycle of the second DC-DC converter module is given by:

d₂＝d₁+Δd' (3)

where Δ d' is the compensation for parameter mismatch between modules, and can be given by:

${\mathrm{\Δd}}^{\′}=(\frac{X_1}{X_2}-1)\·\frac{d_1-d_1^2}{1-2d_1}---\left(4\right).$

8. the method as claimed in claim 6, wherein the current sharing control system comprises two parallel DC-DC convertersSelecting the second DC-DC converter module as the main module and the first DC-DC converter module as the auxiliary module, i.e. making the phase-shift duty ratio of the second DC-DC converter module as the output of the voltage loop regulator, i.e. d₂D, the phase-shifted duty cycle of the first DC-DC converter module is given by:

d₁＝d₂+Δd(5)

where Δ d is the compensation for parameter mismatch between modules, and can be given by:

$\mathrm{\Δ}d=(\frac{X_2}{X_1}-1)\·\frac{d_2-{d^2}_2}{1-2d_2}---\left(6\right).$